Small enough to forget you packed it, loud enough that you won’t.

Why it deserves a permanent spot in your bag
The waterproofing is what turns this from a nice speaker into a useful one. It goes places a normal speaker can’t, which means the beach, the bathroom, the edge of a pool, and the kitchen sink without any of the usual anxiety about splashes.
Size is the other half of it. Small enough to live in a bag permanently rather than being packed deliberately, which is the difference between owning one and actually using one. The sound carries further than something this size suggests it should, and it charges quickly enough that a flat battery is rarely a real problem.
One of those things that quietly improves whatever you were already doing.
TRY IT FOR
In the shower: The original argument for a waterproof speaker, and still the best one.
At the beach or the pool: Sand and splashes are survivable, which rules out almost every alternative.
In a hotel room: Rooms are quiet in a slightly unsettling way. Two minutes of music fixes it.
Cooking dinner: Loud enough over a running tap and an extractor fan, which is a lower bar than it sounds and most small speakers fail it.
